The present invention relates to detecting fires by image processing, in general, and more particularly to an apparatus that detects a fire in a scene by infrared (IR) radiation image processing.
Currently, there are many different methods for detecting fires. One method includes monitoring a predetermined area of interest with an IR radiation detector or an ultraviolet (UV) radiation detector or a combination of the two. Each detector receives the total radiation from the area of interest and generates an electrical signal representative of the total radiation received which may in turn be compared to a threshold value. Exceeding the threshold value by one or more of the detectors generally causes an alarm to be generated that indicates fire is present in the area of interest. While this method detects fires adequately, it is vulnerable to detecting radiation from objects or regions that are not fires and causing undesirable false alarms.
To reduce the number of false alarms, recent fire detection systems have become more sophisticated. Some systems, like the system disclosed in U.S. Pat. No. 5,153,722, entitled “Fire Detection System” and issued Oct. 6, 1992, for example, use image processing of video color image frames of a viewed area to detect one or more regions of fire therein. More specifically, images from the visible light camera are evaluated to identify bright regions which are tracked through sequential frames to determine if any of these regions meet the criteria of a fire event. IR and UV detectors are used to confirm a fire event. Accordingly, fires in the viewed area are determined with a high degree of accuracy.
These visible light camera systems are well suited for large, open air environments in which smoke and other fire byproducts do not obscure the visible images of the camera. However, for fire detection in enclosed areas like cargo bays of aircraft, for example, smoke may quickly fill the enclosed area and prevent the detection of an underlying fire. It is further possible for fog or mist which may be present in aircraft cargo bays due to the environment around the plane to obscure the visible images and prevent the detection of an underlying fire. Even in clean air environments, visible light camera systems may not detect a smoldering fire before it bursts into flames. Also, if a fire commences within the contents of a box or container, it may not be detected by visible image processing until the box or container itself bursts into flames or the flames of the fire escape the box or container, and in these cases, the fire would be permitted to reach a dangerous stage before detection. Accordingly, only flames can be detected using visible light camera systems. Thus, a smoldering fire in a box or container which never reaches the flaming stage may not be detected or confirmed.
The present invention is directed to an apparatus that detects fires through image processing which overcomes the drawbacks of the present methods, especially for enclosed areas, and provides for distinguishing between types of fires.
In accordance with one aspect of the present invention, an apparatus that detects a fire in a scene by infrared radiation image processing includes a means for receiving a sequential plurality of infrared radiation images of the scene. a means for generating for each said image an array of picture elements (pixels), a means for determining for each pixel a value that is representative of the pixel's portion of infrared radiation intensity in the array of the scene image, means for determining a threshold value from the values of the pixels of at least one image, means for identifying a region of at least one pixel in one image of the plurality of images of the scene by comparing the values of the pixels of the one image to the determined threshold value, means for tracking said region through images of the plurality subsequent said one image to determine a change of said region that meets predetermined infrared radiation criteria, and means for detecting the fire in the scene based on the determined change of said region.